Determination of Serological Immunity to Epidemic Typhus by Response to Vaccine

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Abstract
The serological findings obtained from 123 persons have been analyzed. The titers in the complement fixation test before and 10 to 13 days after a single injection of epidemic typhus vaccine of satisfactory potency have been correlated with records of immunization, and residence in typhus or non-typhus zones. From these studies a set of criteria for the epidemic typhus vaccine response have been described. It is concluded that the typhus vaccine response test is more sensitive than other procedures including the complement fixation and mouse toxin neutralization tests for identifying past exposure to epidemic typhus, either by infection or by immunization. A positive history of epidemic typhus in an adult living in an area where epidemic typhus fever has frequently occurred may be fairly reliable. A negative clinical history, even from an adult, is not reliable. In the case of persons who may have been exposed to epidemic typhus prior to age 15 a negative history has little or no validity. The typhus vaccine response test has potential value for epidemiological studies in which it is necessary to determine which individuals in a population have serological immunity to epidemic typhus fever.